Nephrologists possess few treatments to prevent chronic glomerular disease from progressing to renal failure. The limited efficacy of these treatments prompts continuing efforts to identify the mechanisms responsible for disease progression. In chronic glomerular disease, the role of progression is strongly correlated with the amount of proteinuria. Recent studies have suggested that proteinuria causes tubular and then interstitial injury. The goal of the proposed studies is to better understand the mechanisms by which increasing glomerular protein filtration effects the tubule. Understanding of these mechanisms should ultimately facilitate design of therapies to slow renal disease progression. The first aim is to assess the effect of increased protein filtration on proximal tubule endocytic function. Filtered proteins are taken up into tubule cells by endocytosis. Endocytic function, however, has not been studied in proteinuric animals. The proposed studies will employ morphometric techniques to determine whether the tubule responds to increased glomerular protein filtration by increasing the rate of endocytic membrane cycling. Additional studies will examine the effect of increased protein filtration on key molecular components of the endocytic apparatus. The second aim is to examine whether tubular injury can be limited by blocking endocytosis of filtered proteins. At present, pharmacologic therapies to block endocytosis are not available. Studies to test the contribution of endocytosis in tubular injury will therefore be carried out in mice. The development of renal disease will be assessed in recently developed mouse strains in which tubular protein endocytosis has been reduced by gene knockouts. The third aim is to determine whether interstitial inflammation exacerbates tubular injury initiated by increased protein filtration. Tubular injury in proteinuric renal disease is invariably accompanied by interstitial infiltration of T cells and macrophages. The proposed studies will determine whether blocking chemokine signals responsible for cellular infiltration reduces the extent of tubular injury and interstitial fibrosis. These studies, like those of endocytosis, will employ knockout mice to assess the importance of potential mediators of injury which are not yet subject to pharmacologic manipulation.